The present invention relates to bismuth-based pigments exhibiting greatly improved coloring and resistance characteristics.
The invention also relates to the process for producing these pigments and to their application, in particular in the coloring of paints, lacquers and/or plastics.
Technological Background and State of the Art
Bismuth vanadate is a yellow inorganic pigment well known (DE 422447, U.S. Pat. No. 3,843,554, U.S. Pat. No. 4,115,142, JP 62277485 and DE 19733584) for coloring plastics and paints, as a catalyst in the oxidation of olefins, as a contrast-enhancing pigment for television screens and as a reversible temperature indicator.
However, pure bismuth vanadate (named PY184) does not make it possible to directly obtain orange colors. There thus currently exists an obvious need to have available bismuth-based inorganic pigments exhibiting, on the one hand, a color range extending from greenish yellow to orange yellow and having, on the other hand, resistance at least equal to or even superior to those of pure bismuth vanadate.
Pigments based on bismuth vanadate are nontoxic, have a vivid yellow color, have a high coloring strength and have excellent opaqueness; they are readily dispersed in their medium of use and they can be easily used in all kinds of paints (conventional, industrial, powdered).
Bismuth-based pigments with the chemical composition BiOCl are also known (U.S. Pat. No. 2,974,053, DE 3738114 and U.S. Pat. No. 3,917,671). However, these pigments are very different from pigments based on pure bismuth vanadate since they are pearlescent, off-white and rather unresistant to light. They are mainly used in the cosmetics industry for pearlescent and metallic effects.
It is also known, by Patent Application EP-A-632 110, to precipitate a fine layer of bismuth vanadate on a synthetic mica-based pearlescent pigment in order to obtain highly dispersible and very glossy pigments with a yellow hue.
A description has also been given, in Patent Application EP-A-839 874, of basic bismuth vanadates BiVO4.xBi2O3, the yellow color of which verges on orange, either by calcining a very homogeneous mixture of bismuth and vanadium oxides or by calcining a precipitate obtained by the aqueous route in the presence of phosphate.
Other attempts have been made to obtain bismuth vanadates with a reddish hue, by doping the BiVO4 crystal with very small amounts of metals (iron, rare earth metals), but the purity of color and the coloring strength of which leave something to be desired (DE 19529837).
It is also known, by Patent Application DE 197481423, to crystallize bismuth oxide Bi2O3 in a special metastable xcex2 variety by carrying out the process very rapidly in a refluxing aqueous medium in the presence of alkaline hydroxides, to isolate a reddish yellow.
A description is given, in Patent Application EP-A-816 440, of a mixture of pigmentary bismuth vanadate powders and of orange, red or orange yellow organic pigments, to obtain an orange powder which is a pigment with a hybrid inorganic-organic nature.
There also exist other possibilities for obtaining bismuth-based compounds with a darker color, for example by calcining bismuth, zirconium and chromium coprecipitates (DE 4002943).
However, none of these attempts to obtain bismuth-based orange pigments succeed in simultaneously combining the various characteristics desired for an application of a pigment, namely a pure orange color, easy application, nontoxicity and improved resistance to light, to weathering and to heat.
Aims of the Invention
The present invention aims to provide bismuth-based pigments which exhibit a sufficiently pure color of yellow to orange type and which have excellent qualities of resistance.
Another aim of the present invention is to provide bismuth-based pigments, which are easy to apply, in conventional formulations (solvents) and modern formulations (powdered, dispersed in water, with a high solids content, and the like).
An additional aim of the present invention is to provide a process for the manufacture of such pigments which is simple in conception and applicable industrially.
Characteristic Components of the Invention
The invention relates to bismuth-based pigments exhibiting a yellow to orange color composed of a yellow component based on bismuth vanadate and of an orange component based on bismuth oxyhalides which are very intimately combined.
The pigments of the invention correspond to the following general formula:
BiV(1xe2x88x92n)XnO(4xe2x88x923n),
or more particularly to the formula:
(1xe2x88x92n){BiVO4}.n{BiOX},
where:
X denotes a halogen selected from the group consisting of chlorine, bromine and iodine, preferably bromine or iodine, or a mixture thereof, preferably a mixture of bromine and iodine (this mixture furthermore being preferred to bromine alone or to iodine alone)
n is greater than zero and less than one (0 less than n less than 1), preferably between 0.25 and 0.40,
more particularly with n=0.3, that is to say BiV(0.7)X(0.3)O(3.1),
Xn can be written [Cl(p)Br(q)I(1xe2x88x92pxe2x88x92q)]n, in which the situation will preferably be:
between 0 and 0.3,
q between 0 and 0.8 and
p+q between 0.1 and 0.8,
more particularly p=0 and q is between 0.35 and 0.55.
Consequently, in addition to the orange color not possessed by pure bismuth vanadate, the intimate mixing of the two compounds BiVO4 and BiOX gives the pigment of the invention [BiV(1xe2x88x92n)XnO(4xe2x88x923n)], which has durabilities (especially to light) which are improved with respect to the known properties alone of the compounds BiVO4 and BiOX used alone.
In the case where n=1, the compounds present are bismuth oxyhalides BiOX, such as disclosed in U.S. Pat. No. 4,252,570, exhibiting white, yellow, orange and red colors according to the respective contents of various halogens. These contents are given by the coefficients p and q in the following formula BiOCl(p)Br(q)I(1xe2x88x92pxe2x88x921), preferably with p=0.
In this case, the greater the content of iodine, the more the color tends towards orange and reddish. Often, q is taken between 0.35 and 0.55 and preferably between 0.40 and 0.45.
In the case where n=0, the compound present is pure bismuth vanadate BiVO4 (PY184) with a greenish yellow color.
Another aspect of the present invention relates to a pigment having the abovementioned general formula where n=1, that is to say a bismuth oxyhalide BiOX, stabilized and coated with additional protective layers, that is to say comprising one or more successive coating deposits based on oxides, hydroxides, hydrates, carbonates, phosphates, borates, molybdates and/or silicates of elements from Groups II, III and IV (IIIa, IIIb, IVa and IVb) of the Periodic Table, in particular on various compounds based on titanium, aluminum, calcium, zinc, rare earth metals and/or silicon.
The pigments of the invention advantageously corresponding to the abovementioned general formula can also comprise one or more stabilizing or coating layers composed of one or more successive deposits of these said oxides, hydroxides, hydrates, carbonates, phosphates, borates, molybdates or silicates of elements from Groups II, III and IV, in particular those mentioned above.
Said pigments can comprise one or more layers particularly suited to improving the resistances to light, to weathering and to heat of pigments, in particular a final layer based on zinc and boron which makes it possible to improve the resistance to heat and which makes possible its application in materials subjected to high temperatures.
The various inorganic compounds used in the coating layers of the invention can also be prepared from other preferred elements, such as titanium, aluminum, zinc, antimony, silicon, boron, calcium, zirconium, niobium, rare earth metals, in particular cerium, lanthanum, neodymium, praseodymium, samarium or yttritim, or a mixture of these. The proportion (calculated with respect to the total weight of the pigment obtained) of the coating layer or layers is generally between about 1 l and about 30% (wt) (compared to the total wt composition being 100%).
Another aspect of the present invention relates to a process for the manufacture of the pigments of the invention, which is carried out by precipitating bismuth oxyhalides from an acidic bismuth nitrate solution and from a basic solution of alkaline halides. The precipitate obtained is subsequently treated by means known per se to a person skilled in the art for rendering it fine and crystalline. Simultaneously, a pure bismuth vanadate is prepared; the two precipitates are mixed in an aqueous medium, which two precipitates are intimately combined, and homogeneous pigmentary particles are thus formed. The various compounds are present in proportions so as to correspond to the preferred compounds of the invention identified in the above formulae. Preferably, said particles formed are subsequently coated with one or more stabilizing (or coating) layers as defined above. Bismuth-based pigments are thus obtained with an orange yellow color which are very durable, which are very easy to disperse and which can be used to color both plastics and paints of all kinds. The coating of the pigmentary particles is carried out according to the well known process for stabilizing bismuth pigments, for example by the successive deposition of the various coating layers, as mentioned above, or preferably carried out according to the process disclosed in European Patent Application 99 870 193.2, incorporated below by reference.
According to a preferred embodiment of the invention, an orange bismuth oxyhalide is precipitated by bringing together two solutions: the first is acidic and comprises a bismuth salt, generally nitrate; the second is basic and comprises alkaline halides, for example alkali metal chloride, bromide or iodide; the sodium or potassium salts are preferably taken. The bismuth oxyhalide precipitate acquires a pigmentary value if it is left to mature by stirring in an acidic medium and prolonged standing (about 1 to about 20 hours). Subsequently, it can be slightly stabilized by depositing a fine inorganic layer of aluminum phosphate at its surface.
A greenish yellow bismuth vanadate precipitate is also manufactured by reaction of an acidic bismuth salt (generally bismuth nitrate) in the presence of a pentavalent vanadium salt (for example according to the description of Patent WO 94/01497).
When the bismuth vanadate is formed at a pH of the order of about 7.0, the bismuth oxyhalide slurry prepared previously is added and stirring is continued at approximately 90xc2x0 C. for a period of time preferably between about 10 and about 180 minutes. A suspension of very homogeneous orange yellow particles, formed by the intimate combination of the bismuth vanadate and the bismuth oxyhalide, is then obtained.
The pigment obtained can be isolated, but it is preferably subsequently coated with protective and stabilizing layers in order to obtain an orange yellow pigment exhibiting optimum durabilities. The protective layers are those commonly used for inorganic pigments and especially for bismuth vanadates. Successive precipitations are carried out of inorganic compounds deriving from elements from Groups II, III and IV.
The best results are obtained with oxides, hydroxides, phosphates, silicates or molybdates of calcium, zinc, rare earth metals, aluminum, titanium or silicon. In order to obtain optimum deposition, the pigmentary suspension is finally neutralized to a pH of about 7; the pigment is isolated by filtration, washing with water, drying in a conventional way (100 to 400xc2x0 C.) and final milling.
Use may be made, as trivalent bismuth salt, of bismuth nitrate, bismuth carbonate, bismuth acetate and any other solution of these salts sufficiently acidified in order not to be hydrolyzed. Use is generally made of an aqueous solution of bismuth nitrate Bi(NO3) 3.5H2O in nitric acid.
Use may be made, as vanadium source, of combinations of pentavalent vanadium, such as, for example, the oxide, V2O5, or vanadates, Na3VO4, NaVO3 or NH4VO3.
Alkali metal derivatives are used as source of halides; use is made in particular of ammonium, sodium or potassium chlorides, bromides and iodides: NH4Cl, NH4Br, NaCl, NaBr, NaI, KCl, KBr or KI, and preferably potassium iodide and potassium bromide.
Use is mainly made, as source of aluminum phosphate, of aluminum sulfate, chloride or nitrate and alkaline aluminates, on the one hand, and phosphoric acid and alkaline phosphates (alkali metal mono-, di-, tri-, pyro- or metaphosphates), on the other hand.
Use is in particular made, as molybdenum source, of sodium molybdate, Na2MoO4.2H2O, or ammonium molybdate, NH46MO7O24.4H2O.
Any soluble salt, such as, for example, the chloride, CaCl2.2H2O, the nitrate, Ca(NO3)2.4H2O, and the acetate, Ca(CH3COO)2.H2O, can be taken as calcium source.
Another advantage of the pigments of the invention is their ease of use, for example in powdered paints, and their excellent dispersibility in colored formulations.
A final aspect of the present invention relates to a method of coloring of industrial coatings, in particular, resins, lacquers and/or plastics comprising the step of adding the pigments of the invention to said coatings.
The following examples serve to illustrate the various nonlimiting aspects of the invention.